Production of greases having elevated dropping points



' PRODUCTION OF GREASES HAVING ELEVATED DROPPING POINTS George Alwyn Parry, Leatherhead, and John Bryant Matthews, Newton Park, Chester, England, assignors to Shell Development Company, Emeryville, Califi, a corporation of'Delaware No Drawing. Application November 7, 1952,

Serial No. 319,413

Claims priority, application Great Britain January 30, 1952 Claims. (Cl. 252-421) This invention relates to a process for the production of lubricating grease compositions. More particularly, it is concerned with the preparation of greases gelled with soaps and having substantially increased dropping points as compared with greases prepared by other methods.

Soap greases are normally produced by heating aliphatic carboxylic acid soaps or the material to form said soaps, (such as fat and alkali) in the presence of a lubricating oil so as to forma hotfiiud composition in which the soap is dissolved or highly dispersed throughout the oil and subsequently cooling the composition to a gelling temperature. In many instances the gel must then be milled further to produce a satisfactory grease structure, but this is not always essential.

One of the shortcomings of many types of such' greases is their tendency to oxidize and to permit corrosion of metallic parts with whichthey come in contact. These disadvantages are overcome to a substantialdegree by the incorporation of certain anti-oxidants and corrosion preventive agents. The latter class is exemplified by nitrites such. as metallic nitrites or amine nitrites. Hcretofore the additives of this character have been ordinarily added to; permit or cause corrosion.

2,738,329 Patented Mar. 13, 1956 .ture above the gelling temperature of said grease. More particularly, it has been found that the dropping point is raised as much as 40-100 C. by heating a soap and lubricating oil to a hot. fiuid condition and adding a nitrite thereto prior to cooling the composition to a gelling temperature.

Further, in one phase of the present invention a process is devised in which the nitrite is present during the saponification stage. This comprises adding a nitrite to a mixture of a lubricating oil, .a fat (orv fatty acid) and a saponifying agent for the latter, heating to elfect saponification of the fat or fatty acid and to a temperature at .which the composition is fluid and thereafter cooling to a gelling temperature. In this latter process the nitrite may be added either before .or during the saponification process. It may also be added after saponification is complete but while the composition is still fluid and has not been cooled to attain a grease structure.

The ingredients used in the present composition comprise grease-forming amounts of metallic soaps of aliphatic monocarboxylic acids, a lubricating oil and a corrosion protective amount of a nitrite. Normally, grease compositions meeting these requirements contain from about 2 to about 40% by weight of a soap, and 1-5 by weight of a nitrite, the balance comprising lubricating oil together with optional additive amounts of other minor ingredients such as anti-oxidants and the like. Preferably, the compositions comprise from about 5 to about 20% of soap and contain from .2 to 4% of an inorganic nitrite dispersed in a mineral lubricating oil.

The soaps which may be used in the present process comprise the metal soaps of higher aliphatic monocar- The use of soap greases is ordinarily limited by the 7 phase changes which occur in the soap even at relatively mild elevated temperatures. Due to changes in the crystal form of the soaps the greases rapidly soften when hot .and often run out of bearings which they are lubricating. Consequently, fillers must be added to the greases or other types of greases must be utilized when high operating temperatures are expected. This disadvantageous property may be predicted -to a large extent by testing the grease for its dropping point. In general, it appears that the higher the dropping point of the grease the better its high temperature operating characteristics willbe.

It is an object of the present invention .to provide a process for the production of improved grease compositions. It is another object of this invention to provide improved greases containing soaps of fatty acids or ofhydroxy fatty acids and corrosion protective amounts of nitrites. It is a particular object of the present invention to provide greasecompositions exhibiting improved high temperature properties. Finally, it is an object to provide a process for the preparation of greases having improved dropping points. Other objects will become apparent during the following discussion. r

j Now in accordance with the present invention it has been found that the dropping point of greases gelled with .soapsof aliphatic carboxylic acids is substantially elevated to an unexpected degree by the incorporation or presence of a corrosion preventing amount of a nitrite ata temperasuch as vegetable and animal oil glycerides.

boxylic acids, particularly those having at least 8 carbon atoms per molecule and preferably, having between 10 and 24 carbon atoms per molecule. The two principal classes of acids falling Withinthis general class comprise the fatty acids and the hydroxy derivatives thereof, the species of which are well known in the grease forming art as shown, for example, in the book by Klemgard entitled Lubricating Greases. The acids may be derived from natural sources, in which case saponification may take place prior to incorporation with lubricating oil, or the soaps may be formed in situ.

. Typical sources of such acids comprisethe fatty oils The acids may be either saturated, such as stearic acid, or unsaturated, such as oleic acid. Hydroxy fatty acids are especially suitable for certain types of greases and may be derived from castor oil by hydrogenation thereof to form 12-hydroxy stearic acid. Other suitable acids include 9,10- dihydroxy stearic acid; 4-hydroxy palmitic acid; 12-hydroxy-9-oleic acid; linoleic acid; hydrogenated fish oil acid-s; palm oil acids; cottonseed oil acids and the like.

Preferably, alkali metal soaps of these acids are employed, such as those derived from sodium, lithium or potassium. However, the alkaline earth metals and ampheteric metals are likewise suitable, including calcium, barium, strontium, magnesium, aluminum and the like. Typical soaps therefore comprise sodium stearate, lithium-12- hydroxystearate, calcium palrnitate, aluminum stearate, zinc oleate, and lead-l2-hydroxystearate, as well as mixtures of these soaps,,such as mixtures of sodium and cal- I cium soaps. The soap-s may be further modified by the presence of salts of low molecular weight fatty acids to form what are believed to be complexes as in the case of calcium stearate-calcium acetate.

The lubricating oils forming the major ingredient of the presentcompositions are normally mineral oil lubricants which may be derived'from distillate fractions or from residual fractions, such as bright stock. Since the present greaseshave enhancedadrop points and hence are especial- 1y useful for high temperature grease lubrication, it is preferred that the lubricating oil is a bright stock having reasonably high flash and fire points and as low as possible an evaporation rate constituent with the other physical properties of the oil. Preferably, the bright stock has a viscosity between about 1250 and about 11,000 SUS at 100 F. and contains less than about by weight of aromatic hydrocarbons. Suitable bright stocks have viscosity indices above +60 and preferably between 85 and 110. They have flash points above 475 F. and preferably above 500 F.

In addition to the mineral oils to be used in greases prepared by the subject process synthetic lubricants may be present either as the entire lubricating component or as a portion thereof. Suitable synthetic lubricants comprise the aliphatic esters of aliphatic dicarboxylic acids, such as bis(2-ethylhexyl) sebacate, bis(dinonyl) adipate; esters of silicic acid, such as the tetraalkyl silicates, including tetra (isooctyl) silicate; the thia and thio derivatives thereof; esters of phosphorus acids, including the phosphates, phosphouates, and phosphinates, as well as the phosphine oxides. Typical members of these classes comprise trioctyl phosphate, and tri(3,5,5-trimethylhexyl) phosphate; dihexylbenzene phosphonate; and dioctyl(3,5-trimethylhexane) phophate; heptane phosphinate. Other suitable synthetic lubricants comprise the polyalkalene oxides and glycols, preferably having average molecular weights between about 250 and 2500. These may be copolymers or homopolymers and the individual polymer chains may bear hydroxy, ether, or ester radicals. Typcial species comprise the copolymers of ethylene oxide and propylene oxide bearing a methylhexyl radical or at least one of the terminals. Other suitable polymers are those of trimethylene glycol as well as copolymers of ethylene gycol and trimethylene glycol.

In carrying out the process of the present invention the precise conditions employed, especially with respect to temperature, will vary with the identity and proportion of the ingredients. Under normal circumstances the components of the compositions or the mineral oil and soap forming ingredients are heated to temperatures above about 300 F. and preferably above 330 F. to as high as about 450 F. at which temperature saponification is completed and the ingredients are substantially dehydrated.

Under these conditions the ingredients comprise soap and oil forming hot fluid to which the nitrite is added. Thereafter, depending upon the cooking time and temperature as well understood in the art, the composition is cooled to a gelling temperature either dynamically or statically, as the case may be. The gellation temperature is usually below about 270 F., but for the purpose of the present process is not as necessary to define, since the dropping point benefits are gained by the addition of the nitrite to the composition while the latter is in a hot fluid condition. The temperature ranges recited are those employed at normal atmospheric pressure. These will be appreciably lower at elevated pressures such as those encountered in an autoclave, the essential requirement being that the composition is in a hot fluid condition during or following nitrite addition.

Nitrites which may be employed in the present process comprises especially the alkali metal nitrite, such as sodium, potassium or lithium nitrites or the polyvalent metal nitrites, including calcium, barium, aluminum or lead nitrites. In addition thereto the nitrite salts of amines may be utilized, such as Z-aminobutane nitrite, cyclohexylamino nitrite, morpholine nitrite, dibenzylamine nitrite, and trimethylhexyl ammonium nitrite.

The exact action which occurs when the nitrite is added to the grease-forming ingredients while they are in a hot fluid condition has not been clearly determined. The result of whatever action does take place is clearly evident upon determination of the dropping point of the grease resulting from this process. This is especially eviand hexyldi- Example I The following ingredients are mixed and charged to an autoclave to a temperature of 250-260 F. and 55 lbs./sq. in.

Parts by weight Mineral lubricating oil, viscosity Redwood I at 140 F. 50 seconds 61 Mineral lubricating oil, viscosity Redwood I at 140 F. 500 seconds 20 Stearic acid 17 Sodium hydroxide 2 Sodium nitrite 2 The contents of the autoclave are then discharged into an open kettle and stirred down to 158 F. The product is a smooth, shiny grease, brown in color. It has a drop point above 220 C. and a worked penetration of 288.

In comparison with this a grease can be prepared with the above ingredients in the proportions stated, but the sodium nitrite is added in the open kettle after a grease structure is formed. The product is fibrous, grainy and a dark straw color. It has a drop point of only 136 and a worked penetration of 247.

From the above it can be seen that the process of the invention results in agrease having a greatly improved high temperature property evidenced by the considerably higher dropping point.

Example ll 93 parts by weight of bright stock is mixed with 6 parts of lithium, 12-hydroxystearate and 1 part of lithium nitrite. These ingredients are heated to a temperature of 390-420 F. and held at this temperature for about minutes. The temperature is then reduced to a temperature of about 330 for the purpose of permitting gellation to occur. The grease which occurs from this process has a dropping point approximately -80 C. higher than if the lithium nitrite is added after gellation has taken place.

Example 111 90 parts by weight of bis(2-ethylhexyl sebacate are mixed with 8 parts by weight of lithium stearate and 2 parts of lithium nitrite. The ingredients are heated to a temperature of about 410 F. for a period of about 1 hour until a homogeneous solution is formed and then cooled at a rate of about 4 F. per minute to a temperature of about 230 F. The composition is allowed to isothermally gelat this temperature for about 2 hours and then is cooled to room temperature and milled. The resulting grease has a dropping point of about 70 C. higher than that obtained by addition of lithium nitrite to the other ingredients during the isothermal gelling period.

Example IV Bright stock is mixed with stearic acid, aluminum hydroxide and aluminum nitrite at a temperature of about 380 F. for a period of about 2 hours until a hot fluid composition is formed and the water has been removed by distillation. The fluid grease is then cooled to a temperature of about 230 F. and stirred at aboutthis temperature until a grease structure is formed. The droping point of this grease is approximately C. above that obtained when a similar grease is prepared by addition of aluminum nitrite after the soap and oil have been cooled to 230 F.

Example V A copolymer of ethylene oxide and propylene oxide having an average molecular weight of about 1250 is heated together with lime and hydrogenated fish oil fatty acids, calcium nitrite and calcium acetate at a temperature of about 390 F. for a period of 1 hour to form a hot fluid composition which is then cooled with stirring to 210 F. and held at this temperature for a period of. about 1 hour. The grease which results from this process has a substantially higher dropping point than that obtained by addition of calcium nitrite to the grease during the cooling period. The resulting grease had the following composition:

Parts by weight Copolyrner 90 Calcium soap 7 Calcium acetate 2 Calcium nitrate 1 Example VI The process of Example I can be repeated, substituting dicyclohexylamine nitrite for sodium nitrite, thereby obtaining approximately the same degree of advantage with respect to elevation in dropping point.

We claim as our invention:

1. In the process for the preparation of grease compositions wherein a soap of a higher aliphatic monocarboxylic acid is heated with a lubricating oil to form a composition in a hot fluid condition and then cooled to a gelling temperature whereby a grease composition is formed, the improvement comprising adding a nitrite to said composition while it is in a hot fluid condition.

2. In the process for the preparation of grease compositions wherein an alkali metal soap ot a higher aliphatic monocarboxylic acid is heated with a lubricating oil to form a composition in a hot fluid condition and then cooled to a gelling temperature whereby a grease compo sition is formed, the improvement comprising adding a nitrite to said composition while it is in a hot fluid condition.

3. In the process for the preparation of grease compositions wherein a soap of a higher aliphatic monocarboxylic acid is heated with a lubricating oil to form a compo sition in a hot fluid condition and then cooled to a gelling temperature whereby a grease composition is formed, the improvement comprising adding an inorganic nitrite to said composition while it is in a hot fluid condition.

4. In the process for the preparation of grease compositions wherein a soap of a higher aliphatic monocarboxylic acid is heated with a lubricating oil to form a composition in a hot fluid condition and then cooled to a gelling temperature whereby a grease composition is formed, the improvement comprising adding an amine nitrite to said composition while it is in a hot fluid condition.

5. In the process for the preparation of grease compositions wherein a soap of a higher aliphatic monocarboxylic acid is heated with a lubricating oil to form a composition in a hot fluid condition and then cooled to a gelling temperature whereby a grease composition is formed, the improvement comprising adding an alkali metal nitrite to said composition while it is in a hot fluid condition.

6. In the process for the preparation of grease compositions wherein a sodium soap of a higher fatty acid is heated with a lubricating oil to form a composition in a hot fluid condition and then cooled to a gelling temperature whereby a grease composition is formed, the improvement comprising adding a sodium nitrite to said composition while it is in a hot fluid condition.

7. In the process for the preparation of grease compositions wherein an alkali metal soap of a higher fatty acid is heated with a lubricating oil to form a composition in a hot fluid condition which is then cooled to a gelling temperature whereby a grease structure is formed, the improvement comprising adding from about 1% to about 5% by weight based on the grease composition of an alkali metal nitrite to the composition while it is in a hot fluid condition.

8. In the process for the preparation of grease compositions wherein an alkali metal soap of a higher hydroxy fatty acid is heated with a lubricating oil to form a composition in a hot fluid condition which is then cooled to a gelling temperature whereby a grease structure is formed, the improvement comprising adding from about 1% to about 5% by weight based on the grease composition of an alkali metal nitrite to the composition while it is in a hot fluid condition.

9. In the process for the preparation or" grease compositions wherein an alkali metal soap of a fatty acid is heated with a lubricating oil to a temperature above 330 F. to form a composition in a hot fluid condition and is then cooled to a gelling temperature below about 275 F, the improvement comprising heating the composition to a hot fluid condition in the presence of from about 1% to about 5% by weight of an alkali metal nitrite.

10. In the process for the preparation of grease compositions wherein an alkaline earth metal soap of a higher aliphatic monocarboxylic acid is heated with a lubricating oil to form a composition in a hot fluid condition and then cooled to a gelling temperature whereby a grease composition is formed, the improvement comprising adding an inorganic nitrite to said composition while it is in a hot fluid condition.

References Cited in the file of this patent UNITED STATES PATENTS Woods et al Sept. 15, 1953 

2. IN THE PROCESS FOR THE PREPARATION OF GREASE COMPOSITIONS WHEREIN AN ALKALI METAL SOAP OF A HIGHER ALIPHATIC MONOCARBOXYLIC ACID IS HEATED WITH A LUBRICATING OIL TO FORM A COMPOSITION IN A HOT FLUID CONDITION AND THEN COOLED TO A GELLING TEMPERATURE WHEREBY A GREASE COMPOSITION IS FORMED, THE IMPROVEMENT COMPRISING ADDING A NITRITE TO SAID COMPOSITION WHILE IT IS IN A HOT FLUID CONDITION. 